This invention relates to optical waveguides, and more particularly, to an optical coupler having a hybrid core, a portion of which is an organic material, and an adjacent contiguous portion being an inorganic material.
For many years now, waveguides in the form of optical fibers have received widespread interest for information and data transfer. Fiber-guided modulated light beams are useful in many applications, for example, telecommunications, computer link-ups, and automotive controls. Advantageously, fiber optic linkages have a greater information carrying capacity as compared to metal wires carrying electrical signals. Furthermore, fiber optics are less likely to suffer from external interference, such as electromagnetic radiation.
Typically, optical fibers comprise a light-carrying core, for example an inorganic glass such as fused silica or a polymer such as polymethyl methacrylate, and a cladding material having a lower refractive index than the core. The cladding material serves to confine the light energy within the core and thereby allows propagation of light by a phenomenon generally known as xe2x80x9ctotal internal reflection.xe2x80x9d
Characteristically, glass optical fiber cores have very low optical loss and are generally preferred over polymer waveguides for long distance applications.
As of late, monolithic waveguiding devices have gained popularity. These devices tend to be compact and cost effective to manufacture. Such devices are described by the applicant in U.S. Pat. No. 5,470,692 entitled Integrated optic components issued Nov. 28, 1995. In the ""692 patent an integrated optic component comprises a substrate carrying a layer of polymeric material. The component may be poled so as to be an active component and may be in the form of a ridge guide.
Many monolithic devices having, for example polymer waveguides disposed therein provide a single guided mode, similar to single mode optical fibre. Another class of monolithic waveguiding devices are comprised of waveguides disposed in glass wherein an ion diffused region or a reactive-ion-etched structure overcoated with a cladding can serve as a waveguide core.
Polymer waveguides disposed on a substrate offer some advantages over inorganic glass such as silica, in some respects, however, low levels of signal loss i.e. high transparency of inorganic glass is desirable and preferred to polymer. Polymer waveguides are noted for low transparency, i.e. significant loss; polymer waveguides have a high co-efficient of A expansion and, associated with that a high (negative) thermo-optic co-efficient, and a low thermal conductivity. In contrast, inorganic glass has a high transparency, a high thermal conductivity, and a low (positive) thermo-optic coefficient.
This invention utilizes these differences in the two materials in a synergistic manner by providing a inorganic glass/polymer hybrid core structure that is highly advantageous.
Since polymer waveguides are suitable as active devices, they are also useful in optical switches and couplers.
It is an object of this invention, to provide a waveguide that uses the beneficial characteristics of inorganic glass such as silica, and as well the beneficial characteristics of polymer waveguides, while minimizing the unwanted characteristics of these materials.
For example, it is desired to have a optical waveguide with an active region which is highly thermo-optic active, so that it may be switched, attenuated, or modulated with low power. Notwithstanding, it is desired to have an optical waveguide that under normal transmission is highly transparent, i.e. has little signal power loss. Yet still further, it is desired to have a waveguide wherein the refractive index can be changed relatively efficiently and significantly with minimal power. And yet still further, it is desired to have a waveguide with two different regions, having guided light transmitting cores that have relatively different refractive indices, yet that can be modified by the application of a suitable energy, to lessen or obviate the refractive index difference between the two regions. The latter being significantly useful in optical coupling applications such as this invention.
It is an object of this invention, to provide such a waveguide for a novel optical coupler that has heretofore, not been realized.
It is an object of this invention to provide a coupler that can serve as an MMI coupler or a suppressed MMI device in a controllable manner and dependent upon the application of a control signal.
This invention is not limited to waveguides having a core of a particular shape, however this invention is related to a waveguide having a core having a hybrid of materials having different optical properties contiguously disposed one beside the other.
In a preferred embodiment the contiguous cores consisting of dissimilar materials having dissimilar optical properties have a substantially similar mode field diameter.
In accordance with the invention, a multi-mode interference optical device is provided comprising:
a first waveguide having an input end and an output end and having a glass core;
a second waveguide adjacent to the first waveguide having a hybrid core having a first core section of a first material and a second contiguous core section of glass;
a cladding covering at least some of the hybrid core and some of the first waveguide glass core; and,
a heater coupled to the cladding for relatively varying the refractive index difference between the first section of the hybrid core and the glass core in the first waveguide in a controlled manner, so that the refractive index difference between the glass and the first material is variable between substantially about zero and some number greater than zero in the presence or absence of applied heat.
In accordance with the invention, a multi-mode interference optical device is provided, comprising:
a first waveguide having an input end and an output end and having a glass core;
a second waveguide adjacent to the first waveguide having core having a first core section of a first material;
a cladding covering at least some of the first core section and some of the first waveguide glass core; and,
a heater coupled to the cladding for relatively varying the refractive index difference between the first core section and the glass core in the first waveguide in a controlled manner, so that the refractive index difference between the glass and the first material is variable between substantially about zero and some number greater than zero in the presence or absence of applied heat.
In accordance with the invention an MMI coupler is provided comprising:
a first waveguide core of silica;
a second waveguide core of polymer directly next to and contacting the first waveguide core of silica;
a cladding covering the first and second waveguide core, having a lower refractive index than the silica core; and,
a controllable heater for heating at least a region of the second waveguide core, at least the contacting regions of the first and second waveguide cores defining the length of the MMI coupler.
In accordance with another aspect of the invention, a tunable optical MMI coupler is provided comprising:
a first single mode glass waveguide core with a first refractive index n1 and a second polymer waveguide core having at least a portion contacting and in parallel with the first glass waveguide;
a cladding having a second refractive index n2 covering at least some of the first single mode waveguide and the second polymer waveguide; and, means for varying the refractive index of the second waveguide core to values between n1 and n2.
Advantageously, combining two different polymers or preferably polymer and glass wherein polymer has a high negative thermo-optic coefficient compared with glass which has a small positive thermo-optic coefficient, sufficient tuning can be achieved by the application of heat.
Alternatively tuning can be achieved by applying a voltage to vary the refractive index if an electro-optic polymer is used, or compression may be used as a means of varying the polymers refractive index and providing an index difference between the polymer and adjacent glass region.